As is known, insulin and insulin derivatives are required in considerable quantities for the treatment of the disease diabetes mellitus, and some of them are also produced on an industrial scale. Despite the considerable number of insulin compositions and modifications with different action profiles which are already in existence, there is still a need, because of the variety of organisms with their inter- and intraindividual variations, for other insulin products which in turn have other properties and action characteristics.
Insulin derivatives with a delayed action are described, for example, in EP-B 132,769 and EP-B 132,770. These are specifically derivatives with a basic modification in position B31 of the insulin B chain, of the following formula I: ##STR2## in which R.sup.1 denotes H or H-Phe, R.sup.30 represents the residue of a neutral, genetically encodable L-amino acid, and R.sup.31 represents a physiologically acceptable organic group which is basic in nature and has up to 50 carbon atoms, in whose structure 0 to 3 .alpha.-amino acids are involved and whose terminal carboxyl group which is present where appropriate can be free, in the form of an ester functionality, an amide functionality, a lactone or reduced to CH.sub.2 OH.
Characteristic of these insulin derivatives is an isoelectric point between 5.8 and 8.5 (measured by isoelectric focusing). The fact that the isoelectric point is shifted from the isoelectric point of unmodified natural insulin or proinsulin (at pH=5.4) into the neutral range derives from the additional positive charge(s) located on the surface of the molecule as a result of the basic modification. This makes these insulin derivatives with a basic modification less soluble in the neutral range than, say, natural insulin or proinsulin, which are normally dissolved in the neutral range.
The delaying or depot action of the insulin derivatives with a basic modification, of the formula I, derives from their sparing solubility at the isoelectric point. According to the two abovementioned publications, the redissolution of the insulin derivatives under physiological conditions is achieved by elimination of the additional basic groups, which is brought about, depending on the derivative, by trypsin or trypsin-like and/or carboxypeptidase B or carboxypeptidase B-like and/or esterase activity. The eliminated groups are in each case either purely physiological metabolites or else easily metabolized physiologically acceptable substances.
The abovementioned depot principle resulting from basic modification of the insulin has also been further utilized by the provision and corresponding use of other insulin derivatives with basic modifications, mainly within the A and B chains; cf. for example EP-A 0,194,864 and EP-A 0,254,516.
In the insulin derivatives specified in EP-A 0,194,864, a basic amino acid is incorporated in the B27 position and/or a neutral amino acid is located at positions A4, A17, B13 and/or B21; in addition, the C-terminal carboxyl group of the B chain is blocked by an amide or ester residue.
The insulin derivatives specified in EP-A 0,254,516 are very similar to those specified in the abovementioned EP-A; however, in this case, with the aim of increasing the stability of the relevant pharmaceutical compositions at the weakly acid pH values, the amino acid Ash in position A21 can also be replaced by other amino acids which are more stable in acid medium, such as, for example, Asp. As is known, Ash (=asparagine) differs from Asp (=aspartic acid) by the blocking of one of the two carboxyl groups by the amide group: ##STR3##
Rapid-acting insulin derivatives are said to result from yet another modification of the insulin molecule in the A and B chain, in particular by replacing the amino acid His, which is responsible for the formation of a complex with zinc--and thus for a certain delaying action, in the B10 position by other appropriate amino acids; cf. EP-A 0,214,826.
All the insulin derivatives specified in the 3 lastmentioned publications are mainly modified within the A and B chains; they are prepared by genetic engineering routes.